1. Field of the Invention
The present invention relates to a reverse osmosis system having an accumulator means for receiving and temporarily holding or shunting away any excess backflow water from the associated sewage system. The accumulator means can also be configured to perform a similar function for a higher than normal flow of reject water from the reverse osmosis unit. In either situation the excess water is prevented from reaching and contaminating or flooding the air gap in the system.
2. Description of the Prior Art
Reverse osmosis (RO) units accept source water under pressure from a municipal water supply or the like. The supply pressure forces a portion of the source water through a special membrane to produce potable or high quality drinking water. The water which does not pass through the membrane is waste or reject water which flows into a drain line connected to the sewer system. The typical slow drip flow of the RO reject water is often annoyingly audible to a householder, which is particularly true when the RO unit is located under the kitchen sink.
In many RO units the reject water flows constantly at the slow drip rate, but in more recent RO models the production of potable water is automatically stopped when the potable water tank of the RO unit is full or nearly full. This of course also stops the flow of reject water as well.
Potable water from the outlet of the RO tank typically passes upwardly through flexible tubing to a dispensing faucet located on or above the sink countertop of the household. The reject water has a high concentration of solids and other contaminants and it is directed toward a drain line for emptying into the sewer system. However, it first flows under pressure from the RO unit outlet, through flexible tubing, and then through a system backflow prevention device which meets plumbing code requirements. This is usually an air gap located on the countertop and open to atmosphere for venting.
The reject water flows primarily under the force of gravity through the air gap portion and into a drain line connected to the sewage system. Located as it is between the supply of potable water and the drain line, the air gap portion prevents any vacuum from forming in the system. This prevents back siphoning or backflow of sewage water from the drain line and into contact with the air gap portion.
Sewer water backflowing past the air gap portion of the air gap unit, or backing up into the air gap portion, is considered to have contaminated the water supply or to present likelihood of contamination.
Most plumbing codes specify that an RO air gap unit must be located above the highest level that the rising backwater can reach, which is why it is common to locate the air gap unit on or above the sink countertop, even though this location is often unsightly and does almost nothing to conceal the sound of the dripping RO reject water.
A typical sewer stoppage prevents normal forward or drainage flow of water into the sewer. Consequently, any water from the household, including RO reject water, causes a gradual rising or backflow of contaminated water from the sewer line. Unless there is some provision for stopping this contaminated backflow, or shunting it somewhere, it very quickly reaches and contaminates the air gap. Usually it simply spills out of the air gap portion and onto the kitchen counter or other adjacent surface.
For brevity, the air gap portion is often referred to as the air gap, and the same applies to air gap unit, which is also sometimes referred to as the air gap for convenience.
Obviously, it is desirable to provide a means for preventing contamination of the air gap by such slowly rising drain or sewage water.
Contamination also results from high velocity backflows, such as would occur when a sudden high vacuum in the household water system is caused by opening of a nearby fire hydrant. Such a high velocity backflow is more likely to be caused when a householder uses a plunger, aerosol "bomb" or the like to develop a localized high pressure to try and clear the stoppage.
The localized pressure produces a sudden spurt or surge of contaminated backflowing water that relatively easily spurts across and contaminates the typical air gap. Special air gaps have been devised to prevent this, including the air gap that is disclosed in my U.S. Pat. No. 5,176,165, entitled "Air Gap Apparatus". The patented air gap includes a diverter passage and flow deflector that is effective to channel to atmosphere very rapid or explosive backflows so that they cannot reach or spurt across the air gap and contaminate or potentially contaminate the potable household water supply.
It is only recently that there has been any widespread recognition of the contaminating effect such backflows can have on the air gap in an RO system. A satisfactory way of stopping or safely accommodating such backflow surges is clearly needed.
Simple check valves located downstream of the air gap might appear to be a feasible solution since they would block undesired upstream flow, but plumbing codes prohibit their use for this purpose. The codes are based upon the assumption that after service in drainage systems, check valves cannot be relied upon to seat properly in the presence of foreign materials in such systems.
Check valves are also disadvantageous because they require a spring bias to keep them seated against slowly rising backflow. This also affects normal or drip flow of reject water since the valves would open only when the reject water backs up enough to develop a pressure sufficient to overcome the valve bias.
The reject water flows in such small quantities and at such low flow rates that it will not flow through the typical small bore tubing leading to the drain outlet if there is any kind of obstruction or blockage. A valve that is biased to a closed position looks like a blockage to the forward flowing reject water, and it will cause the reject water to back up and rise enough to reach and contaminate the air gap before the valve opens to empty the reject water into the drain outlet.
The air gap can also be contaminated or overloaded by an excessive forward flow of reject water from the RO unit. In certain recent models of RO units, the special membrane through which source water is forced to produce potable water is automatically periodically purged or flushed. This is done by allowing a relatively high volume of source water to flow over the membrane to flush away foreign contaminants that collect on the membrane surfaces and reduce the efficiency of conversion of the source water to potable water.
Instead of providing oversize plastic tubing and associated fittings and alternate flow passages to accommodate the occasional high flow of flushing water from such an RO unit, it is preferable to continue the use of the lower cost and more easily handled small diameter tubing and fittings used with non-flushing RO units. The smaller tubing is more than adequate to handle normal low flow reject water, which is in the order of about two to five ounces per minute. As will be seen, the present invention provides a means to accommodate the temporary surge of RO purging water without having to increase the size of the drain tubing and the other components in the system.